1. Field of the Invention
The present invention relates to IC (integrated circuit) cards, and, more particularly, to a thin IC card having a number of IC chips mounted thereon.
2. Description of the Related Art
External data storage devices having integrated electronic components such as IC's mounted on a thin card-shaped base substrate are generally known as "IC cards." The IC cards have many advantages over a conventional magnetic card having a magnetic tape for data storage, such as significantly larger memory capacity, higher data accessing speed, and higher reliability in storing data. Because of these merits, there is an increasing demand for IC cards.
According to presently available IC cards, for example, IC memory cards, in mounting IC chips on a card-shaped base substrate, these IC chips are mounted on a thin printed board first. Wire bonding or tape-automated bonding (TAB) is employed in electrically connecting connection terminals (bonding pads) of each IC chip to the wiring pattern on the printed board. With such an arrangement, however, it is difficult to make an IC card compact and thin. The use of the wire bonding needs about 0.2 to 0.5 mm high connection wires, which stands in the way of reducing the depth of IC cards. Irrespective of the use of either the wire bonding or TAB, electric connection between each IC chip and the printed board requires a wiring region having twice as large an area as the IC chip, or more, around each IC chip. This inevitably would enlarge the IC card.
A solution to the above problem is proposed in Japanese Patent Disclosure (KOKAI) No. 61-75488 which discloses IC chips directly embedded in a card base substrate without using any printed board. Here, a conductive paste is used to provide the wiring of the IC chips embedded in the card base substrate. According to the disclosed IC card, however, mounting an increased number of IC chips on the card would make it significantly difficult to align the connection terminals of all the embedded IC chips with the wiring pattern provided by the conductive paste. This shortcoming unnecessarily makes the production process of IC cards difficult and complicated.
Two-piece connectors are typically known as means to connect an IC card to an external reading device. Due to their thickness of 2 to 3 mm, the overall IC card cannot be made thinner even if those portions excluding the connector section can be designed in conformity with the ISO standards.